Micro-film camera

ABSTRACT

A microfilm camera for reproducing documents is provided with a photo receiver mounted on its housing. An optical system mounted on the housing directs light reflected by a punctiform area near the edge of the document to be photographed onto the photo receiver. A wedge prism is rotatably mounted on the housing in the light path between the photo receiver and the document to enable the puntiform portion scanned by the photo-receiver to be varied over the document and its border during a rotation of the wedge prism. Mounted on the housing is a drive means which rotates the wedge at a constant speed. Provision is made for reducing the output from the photo-electric device to a zero illumination level once during each revolution of the wedge prism. Mounted on the housing is a measuring circuit which includes a rectifier connected with an output of the photoreceiver and a storage device having a time constant long compared with the time for one rotation of the wedge prism and effective to store a voltage indicative of the brightness of the document. A control device is influenced by the output of the storage device provides a controlled voltage which influences the illumination of the lamp in dependence on the brightness of the document border.

United States Patent Reimann 1541 MICRO-FILM CAMERA [72] inventor:Hubertus .Reimann, Dresden, Germany [73] Assignee: VEB Pentac on DresdenKamera-und Kino'wierlte, Dresden, Germany v 22 Filed: Jan.4, 1971 21Appl.No.: 103,672

Primary Examiner-Samuel S. Matthews Assistant ExaminerMichael L. GellnerAtt0rney-Young Thompson 1451 Dec. 5127?:

[57] ABSTRACT A microfilm camera for reproducing documents is providedwith a'photo receiver mounted on its housing. An optical system mountedon the housing directs light reflected by a punctifor'm area near theedge of the document to be photographed onto the photo receiver. A wedgeprism is rotatably mounted on the housing in the light path between thephoto receiver and the document to enable the puntiform portion scannedby the photo-receiver to be varied over the document and its borderduring a rotation of the wedge prism. Mounted on the housing is a drivemeans which rotates the wedge at a constant speed.

Provision is made for reducing the output from. the photo-electricdevice to a 'zero illumination level once 4 Claims, 3 Drawing FiguresPKTENTEDMB 5 I972 704- 947 SHEET 2 [IF 2 By racf a.

A HorneyS 1 MICRO-FILM CAMERA. BACKGROUND TO THE INVENTION The inventionrelates to amicro-film camera for reproducing documents, which has anautomatic exposure-control device, wherein the maximum intensity thesubject, an .uninscribed' part of the subject isscanned by aphoto-electric receiver. This applies especially inthe case ofcontinuous cameras and cameras for immobile subjects which are intendedfor different subject formats. Inthe case of continuous cameras the edgeof the subject departs from .the measurement point, while in the. caseofdifferent subject formats the marginal zones of the differentsubject'formats likewise are not always to be expectedjin the sameposition. Thus the necessity arises of storing the measurement resultand using it as constant control value during theentire. exposureoperation.;Fluc tuations of intensity of illumination during theexposure operation cannot be taken into consideration and leadtodifferent negative density qualities, which makes the largement moredifficult;

The invention has the aim of better assurance of -a procedure ofre-enconstant quality of the photographicexposure, and has the object ofdirectlyv compensating any fluctuations of intensity ofilluminationwhich occur during the exposure operation. 7

SUMMARY OF'INVENTION' According to the invention this is achieved in amicrofilm carnerafor reproducing documents with the provision of aphoto-receiver mounted on the-camera I housing, an optical systemmounted on the camera housing for directing light reflected by apunctiform area near to the edge of the document to bephotographed ontothe photoreceiver, a wedge prism rotatably mounted on the housing in thelight path between the photo receiver and the document to enabledifferent punctiformportions of the document and its border to bescanned by the photo receiver during a rotation of the wedgeprism,'drive means mounted on the housing for rotating the wedge atconstant speed, means for reducing the output of the photo electricdevice to a zero illumination level once during each revolution of thewedge prism, a measuring circuit mounted on the housing; including arectifier circuit connected with anoutput of. the photo receiver and astorage device having atime constant long compared with the time for onerotation of the wedge prism effective to store a voltage indicative ofthe brightness of the document, a control devicehaving an inputconnected with the output of the'storage deviceand n output connectedwith a lamp arranged to illuminate the document whereby the illuminationof the document is controlled by the control device in dependence on thebrightness of the document border.

2 BRIEF DESCRIPTION OF DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENT A.subject 2, which may be a document to be reproduced on a film in knownmanner by a picturetaking optical system (not shown), is situated on asubject carrier (not shown) which is non-displaceably arranged ormovable in the direction of the arrow 1. An

inscription image is situated in the middle area 2a of the document 2,while a margin 2b is uninscribed.

Therefore on illumination of the subject the light intensitycorrespondingto the reflection of the base material is reflected by themarginal zone 2b. 7

A photo-receiver 3 is arranged above the subject 2 (see FIG. 1). Beneatha photo-receiver 3 there is situated the diaphragm 4, which permitsadjustment of the light transmitted to the reception surface of'thephotoreceiver 3, so that constant exposure factors, for example the filmsensitivity or filter values, can be introduced. The optical system 9directs light from the document onto the photo receiver which receiverhas only a small surface area sensitive to light so that for example apunctiform measurement point 5 in the marginal zone 2b influences thereceiver. An optical deflection system in the form of a glass wedge 6 isprovided in front of the optical system 9 which wedge refracts the lightpassing through to the photo receiver so that by rotation of the wedgethe measurement point 5 revolves and the portion scanned by the photoreceiver follows a'path 7. The The radius r of the measurement path 7 isdimensioned according to the displacementof the marginal zones to beexpected in the case of different subject formats. The glass wedge 6 isembedded in a mounting 8, which is coupled through a cord 10 with adrive wheel 11 of a motor 12.

Parallel with the photo-receiver 3 a short-circuit switch 13 isprovided. On the mounting 8 a switch cam 14 is arranged which operatesthe switch 13 which short-circuits the photo-receiver 3 during a part ofthe rotation of the glass wedge 6. Thus a value zero can be imitated asa basic light intensity value.

At every revolution of the glass wedge 6 at least one voltage pulseoccurs at the output of the photo-conductive cell, which pulsecorresponds to the light reflected by the base material of the subject,and at least one further voltage pulse occurs therewhich corresponds tothe light reflection value zero of a black subject. A- voltage waveformemitted by the photo-receiver in thecase of the example of embodimentillustrated in FIG. 1 is represented in FIG. 2.

The output of the photo-receiver 3 is connected to analternating-current amplifier 15, to the output of which a peak-valuerectifier circuit 16 is connected. Assuming that the time constant RC ismade large in relation to the period of a complete rotation of the glasswedge 6, a voltage U occurs between the terminals A and B which isproportional to the difference between the reflection capacity of thesubject base and the zero value, that is it constitutes a direct measureof the correct exposure of the subject. After the measuring arrangementhas once been calibrated, a deflection of the pointer of the measuringinstrument 17 is obtained as value for the correct exposure.

For the automation of the exposure adjustment as electronic controlapparatus 18, automatically influences current supplied to anilluminating device and is connected in parallel with the terminals Aand B. This control apparatus ,18 in known manner contains two triggerswith constant but different threshold voltages and without greathysteresis. Each trigger is operative to actuate a respective relay,which relays influence the direction of rotation of a motor. In the caseof correct illumination both relays are at rest. The motor in a knownmanner adjusts a regulating transformer to provide a variable voltagewhich influences the intensity of the lamps 19. In the case ofinsufficient illumination of the subject, indicated by inadequateoutput'voltage between the terminals A and B, one relay is operated byits respective trigger and causes the motor to run in the direction ofrotation that a transformer voltage output increases and the lamps 19light more brightly. This motor rotation lasts until the voltage betweenthe terminals A and B has reached a value which causesThe trigger tode-energizes the relay. In the case of over-illumination the motorrotates in the opposite direction, the rotation being instigated andterminated by the other trigger and respective relay. The controlapparatus 18 may include a regulating circuit in which lamp brightnessis controlled by means of thyristors. ln this case the voltage presentbetween the terminals A and B is effective to control the ignition angleof the thyristors.

The generation of the basic intensity value may be effected byalternating means. By way of example a rotating blade-type diaphragme.g. a sector diaphragm which may be geared with the rotating glasswedge 6 to periodically interrupt the ray path to the photoreceiver 3,preferably with a frequency higher than the frequency of rotation of therotating glass wedge 6. It is also possible for the area situatedoutside the subjects, that is the surface of the subject carrier, to bekept as dark as possible, so that a basic intensity value is achievedduring every scanning period according to a low reflectioncharacteristic of the subject carrier. It is also possible to permit themeasurement point to run on the measurement path 7 lying outside thesubject over an auxiliary light source of constant luminous intensity,which is less than the minimum reflection of the subject base everoccurring. The deflection optical system can also be formed by aswinging mirror.

I claim:

I. In a microfilm camera for reproducing documents the provision or aphoto-receiver mounted on the camera housing, an optical system mountedon the Camerafhousing for directing light reflected by a punctiforrnarea near to the edge of the document to be photographed onto thephoto-receiver, a wedge prism rotatably mounted on the housing in thelight path between the photo-receiver and the document to enabledifferent unctiform ortions of the document and its border to e scannedy the photo-receiver during a .circuit connected with an output of thephoto-receiver and a storage device having a time constant long comparedwith the time for one rotation of the wedge prism effective to store avoltage indicative of the brightness of the document, a control devicehaving an input connected with the output of the storage device and anoutput connected with a lamp arranged to illuminate the document wherebythe illumination of the document in controlled by the control device independence on the brightness of the document border.

2. A microfilm camera according to claim 1 wherein the means forreducing the output of the photo-electric device to zero illuminationlevel comprises a switch adapted to short circuit the photo-electricdevice and a switch cam mounted on the housing and driven by the drivemeans to effect closure of the switch.

3. A microfilm camera according to claim 1 wherein the reduction of theoutput of the photo-electric device to zero illumination level iseffected by the wedge prism which is adapted so that the variableportion scanned overlaps the edge of the document whereby no reflectionoccurs.

4. In a microfilm camera for reproducing documents of the type having asector diaphragm driven by a drive means and effective to block lightpassage to a photoreceiver during each exposure, the provision of anoptical system mounted on the camera housing for directing lightreflected by a punctiform area near to the edge of the document to bephotographed onto the photoreceiver, a wedge prism rotatably mounted onthe housing and coupled to the drive means, which prism is positioned inthe light path between the photo-receiver and the document to enabledifferent punctiform portions of the document and its border to bescanned by the photo-receiver during a rotation of the wedge prism bythe drive means, a measuring circuit mounted on the camera housingincluding a rectifier circuit connected with an output of thephoto-receiver and a storage device having a time constant long comparedwith the time for one rotation of the wedge prism effective to store avoltage indicative of the brightness of the document, a control devicehaving an input connected with the output of the storage device and anoutput connected with a lamp arranged to illuminate the document wherebythe illumination of the document is controlled by the control device independence on the brightness of the document border.

* a s t:

1. In a microfilm camera for reproducing documents the provision or aphoto-receiver mounted on the camera housing, an optical system mountedon the camera housing for directing light reflected by a punctiform areanear to the edge of the document to be photographed onto thephoto-receiver, a wedge prism rotatably mounted on the housing in thelight path between the photo-receiver and the document to enabledifferent punctiform portions of the document and its border to bescanned by the photo-receiver during a rotation of the wedge prism,drive means mounted on the housing for rotating the wedge at constantspeed, means for reducing the output of the photo-electric device to azero illumination level once during each revolution of the wedge prism,a measuring circuit mounted on the camera housing including a rectifiercircuit connected with an output of the photo-receiver and a storagedeVice having a time constant long compared with the time for onerotation of the wedge prism effective to store a voltage indicative ofthe brightness of the document, a control device having an inputconnected with the output of the storage device and an output connectedwith a lamp arranged to illuminate the document whereby the illuminationof the document in controlled by the control device in dependence on thebrightness of the document border.
 2. A microfilm camera according toclaim 1 wherein the means for reducing the output of the photo-electricdevice to zero illumination level comprises a switch adapted to shortcircuit the photo-electric device and a switch cam mounted on thehousing and driven by the drive means to effect closure of the switch.3. A microfilm camera according to claim 1 wherein the reduction of theoutput of the photo-electric device to zero illumination level iseffected by the wedge prism which is adapted so that the variableportion scanned overlaps the edge of the document whereby no reflectionoccurs.
 4. In a microfilm camera for reproducing documents of the typehaving a sector diaphragm driven by a drive means and effective to blocklight passage to a photo-receiver during each exposure, the provision ofan optical system mounted on the camera housing for directing lightreflected by a punctiform area near to the edge of the document to bephotographed onto the photo-receiver, a wedge prism rotatably mounted onthe housing and coupled to the drive means, which prism is positioned inthe light path between the photo-receiver and the document to enabledifferent punctiform portions of the document and its border to bescanned by the photo-receiver during a rotation of the wedge prism bythe drive means, a measuring circuit mounted on the camera housingincluding a rectifier circuit connected with an output of thephoto-receiver and a storage device having a time constant long comparedwith the time for one rotation of the wedge prism effective to store avoltage indicative of the brightness of the document, a control devicehaving an input connected with the output of the storage device and anoutput connected with a lamp arranged to illuminate the document wherebythe illumination of the document is controlled by the control device independence on the brightness of the document border.